KR102579333B1 - Copper ion-exchanged BEA zeolite catalyst and catalytic reaction system for low-concentration methane combustion using the same - Google Patents

Abstract

The present invention discloses a zeolite catalyst in which copper is ion-exchanged and a catalytic reaction system for low-concentration methane combustion using the same. According to the present invention, a zeolite catalyst in which copper is ion-exchanged with acid-type BEA zeolite having a preset SiO ₂ /Al ₂ O ₃ molar ratio is provided for low-temperature combustion of low-concentration methane under ozone conditions.

Description

Copper ion-exchanged BEA zeolite catalyst and catalytic reaction system for low-concentration methane combustion using the same}

The present invention relates to a copper ion-exchanged BEA zeolite catalyst and a catalytic reaction system for low-concentration methane combustion using the same.

As rapid industrialization continues to lead to excessive use of fossil fuels, interest in the development of eco-friendly energy is increasing to reduce the pollutants generated.

Among them, natural gas is attracting attention due to its abundant reserves and economic feasibility. Natural gas is a mixed gas containing methane as a main ingredient and light hydrocarbons such as ethane, propane, and butane, and is mined from gas fields on the sea floor or on land.

Gas mined from gas fields was burned when there was no means of transportation, but with the development of piping technology, long-distance transportation became possible. Natural gas has been difficult to transport and store compared to liquid fuel, so the scope and scope of its use have been limited. However, with the development of the liquefaction process in 1960, the use of natural gas expanded as marine transportation became possible by liquefying gas from the source.

However, as atmospheric emissions of methane, the main component of natural gas, increase, environmental problems such as global warming are emerging.

The greenhouse effect per unit molecule of methane is known to be about 70 times higher than that of carbon dioxide, but it is the most difficult to decompose through oxidation among hydrocarbons due to its strong C-H single bond.

Methane, which has a significant impact on the greenhouse effect, is emitted from various sources, including fossil fuel (coal, crude oil, gas) mining, landfill waste, livestock waste, and natural gas internal combustion engines (cars, ships, etc.).

In particular, a lot of unburned methane emitted from natural gas internal combustion engines is generated under cold start conditions where the temperature inside the engine is lower than normal. When the temperature inside the engine is high and the exhaust gas temperature is above 350°C, the combustion reaction of methane by the catalyst can be smoothly induced by sufficient heat energy supply, but under cold start conditions at the beginning of the engine start, the temperature is low for methane to be burned. This causes the problem that low-concentration methane that has not been reacted is discharged as is.

Pd-based noble metal catalysts are mainly used as effective catalysts for the combustion of low-concentration methane, but due to economic problems due to their high price, research is being actively conducted to replace them with non-precious metal oxide catalysts.

However, non-precious metal-based catalysts generally require high temperature conditions of 350°C or more to burn 50% of methane, and high reaction temperature conditions are disadvantageous in terms of energy efficiency of the post-treatment device and catalyst durability. Therefore, in order to efficiently burn low-concentration methane emitted from various mobile sources (natural gas vehicles) and fixed sources, it is necessary to develop a new concept of catalytic reaction system that uses non-precious metal catalysts and consumes only low energy.

Republic of Korea Patent Registration Publication 10-2044604

In order to solve the problems of the prior art described above, the present invention seeks to propose a copper ion-exchanged BEA zeolite catalyst that can improve low-concentration methane combustion activity at low temperatures and a catalytic reaction system for low-concentration methane combustion using the same.

In order to achieve the above-described object, according to an embodiment of the present invention, copper is ion-exchanged in acid-type BEA zeolite having a preset SiO ₂ /Al ₂ O ₃ molar ratio in order to burn low-concentration methane at low temperature under ozone conditions. A zeolite catalyst is provided.

The low-concentration methane can be burned at a low temperature of 125 to 175 °C.

The Cu/Al molar ratio may range from 0.20 to 0.30.

The concentration ratio of the low-concentration methane and the ozone may range from 1:4 to 1:6.

According to another aspect of the present invention, there is a method for producing a zeolite catalyst for low-temperature combustion of low-concentration methane under ozone conditions, in which zeolite in the form of an ammonium salt is heat-treated at a preset time and temperature to form a preset SiO in which hydrogen cations are bonded to aluminum anions. Converting to acid-type BEA zeolite with _{a 2} /Al ₂ O ₃ molar ratio; Adding and stirring the acid-type zeolite to an aqueous copper nitrate solution; separating the solid phase catalyst through a filtration device; Washing and drying the separated solid phase catalyst; and calcining the washed and dried solid catalyst to prepare a catalyst in which copper is ion-exchanged.

According to another aspect of the present invention, there is provided a catalytic reaction system for low-temperature combustion of low-concentration methane, comprising: a dielectric barrier discharge (DBD) reactor that supplies ozone generated through an oxidation reaction of oxygen or air; And a zeolite catalyst in which copper is ion-exchanged is charged to an acid-type BEA zeolite having a preset SiO ₂ /Al ₂ O ₃ molar ratio, and catalytic combustion in which the low-concentration methane is burned under low-temperature conditions using ozone supplied from the DBD reactor. A catalytic reaction system including a reactor is provided.

According to the present invention, low-concentration methane combustion performance at low temperatures can be maximized by using ozone, which has stronger oxidation performance than previously used oxidizers, and a N ₂ O oxidant that exhibits methane oxidation activity around 200 to 250 ° C. Unlike this, methane combustion performance at significantly lower temperatures can be improved by using ozone, which generates reactive oxygen species at lower temperatures, as an oxidizing agent.

In addition, by implementing methane combustion under low temperature conditions without introducing an additional heat source, the energy efficiency of the post-treatment device can be increased and operating costs can be reduced.

In addition, in the case of the previously reported 20 wt% supported Pd-based catalyst using expensive precious metals, a temperature of 233°C was required to secure 50% methane conversion, whereas when ozone and copper ion exchange zeolite catalyst were combined, 50% % methane conversion rate can be secured under temperature conditions below 125~175°C, so enormous cost savings can be expected by replacing expensive precious metals with copper, a cheap transition metal.

Figure 1 is a diagram showing the manufacturing process of a zeolite catalyst in which copper is ion-exchanged for low-temperature combustion of low-concentration methane according to a preferred embodiment of the present invention.
Figure 2 shows an XRD (X-ray diffraction) graph of a zeolite catalyst in which copper is ion-exchanged according to an embodiment of the present invention.
Figure 3 is a diagram showing the configuration of a catalytic reaction system for low-concentration methane combustion according to an embodiment of the present invention.
Figures 4 and 5 are graphs showing the low-concentration methane combustion performance of a catalyst obtained by ion-exchanging copper with BEA-structured zeolite.
Figures 6 to 9 are graphs showing the low-concentration methane combustion performance of a catalyst obtained by ion-exchanging copper with ZSM-5 zeolite of the MFI structure.
Figure 10 is a graph showing low-concentration methane combustion performance as the concentration of ozone increases from 2,200 to 3,000 ppm according to 500 ppm of methane.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The present invention proposes a copper ion-exchanged zeolite catalyst that can effectively induce a low-concentration methane oxidation reaction by ozone, and suggests the optimal copper ion exchange amount range. In addition, optimal reaction conditions such as reaction temperature at which the catalyst according to this example can show effective activity, ozone concentration compared to methane, and catalyst amount (w/f) compared to the flow rate of supplied gas are presented.

Zeolites are valuable as catalysts, catalyst supports, adsorbents, and ion exchange materials in chemical processes. Zeolite refers to crystalline aluminum silicate oxide (Aluminosilicate), where silicon and aluminum each combine with oxygen to form a tetrahedral structure. The aluminum tetrahedron, in which four oxygen atoms of a divalent anion are bonded to the aluminum of a trivalent cation, has a monovalent anion. Hydrogen cations, ammonium ions, and sodium ions are bound to this anion, but ion exchange with other metal cations is possible.

Metal ions exchanged as isolated species in zeolite can induce the effect of high dispersion of active metals and prevent deterioration of catalytic performance due to thermal agglomeration. In many studies, zeolites with a Si/Al ratio higher than 10 are mainly used because the structural stability of zeolite increases as the Si/Al ratio increases. If the Si/Al ratio is low, the amount of active metal substitution increases due to an increase in ion exchange active sites, which may cause structural instability.

Hereinafter, with reference to the drawings, the manufacturing process of the copper ion-exchanged zeolite catalyst and the low-concentration methane oxidation reaction will be described in detail.

Figure 1 is a diagram showing the manufacturing process of a zeolite catalyst in which copper is ion-exchanged for low-temperature combustion of low-concentration methane according to a preferred embodiment of the present invention.

In this embodiment, low concentration methane is defined as a concentration of 1 volume percent or less in the atmosphere, and may be unburned methane generated under cold start conditions, especially in an internal combustion engine.

First, the zeolite in the form of an ammonium salt is converted into an acid-type zeolite in which hydrogen cations are bonded to aluminum anions by heat treatment for a preset temperature and time under dry air flow conditions (step 100).

Here, the heat treatment temperature and time may be 4 hours at 500°C.

In this example, a catalyst is produced by ion-exchanging copper with zeolites of various structures, and zeolite in the form of sodium salt is synthesized by stirring acid-type zeolite in a sodium nitrate solution at room temperature for 24 hours.

The modified acid or sodium salt zeolite is added to an aqueous copper nitrate solution of appropriate concentration and stirred for 24 hours (step 102).

After completing the stirring, the aqueous solution and the solid catalyst are separated through a filtration device (step 104), and then the catalyst is washed using an excess amount of deionized water (step 106).

Afterwards, it is dried under air conditions at 120°C for 12 hours (step 108), and then calcined at 550°C for 12 hours to prepare a zeolite catalyst in which copper is ion-exchanged (step 110).

Figure 2 shows an XRD (X-ray diffraction) graph of a zeolite catalyst in which copper is ion-exchanged according to an embodiment of the present invention.

Referring to FIG. 2, as only diffraction patterns for the zeolite crystal plane were observed in the absence of undissolved copper precursor (Cu(NO ₃ ) ₂ ) and copper oxide (CuO), copper ions were effectively distributed within the zeolite structural lattice. It can be confirmed that it was highly dispersed and ion exchanged.

The catalyst according to this embodiment is applied to a catalytic reaction system for low-temperature combustion of low-concentration methane, and the catalytic reaction system is a dielectric discharge plasma (Dielectric barrier discharge, hereinafter referred to as DBD) that supplies ozone generated through the oxidation reaction of oxygen or air. The reactor and a zeolite catalyst in which copper is ion-exchanged are charged, and may include a catalytic combustion reactor that burns the low-concentration methane under low-temperature conditions using ozone supplied from the DBD reactor.

In this example, the DBD (Dielectric Barrier Discharge) plasma reactor was composed of a SUS mesh surrounding the outside of the dielectric quartz tube and a copper rod in the center of the cylinder. Using a Power Supplier (Jungwoo System), an alternating current (AC) voltage input with a frequency of 409 Hz and a size of 16.0 kV for the second cut-off was supplied to the DBD plasma reactor, and an oscilloscope (Tektronix TDS 220) was used to supply the The waveforms and sizes of voltage and current were observed.

O ₂ (99.999%) equivalent to 10% of the total flow rate supplied to the reaction was flowed into the plasma reactor, and the ozone concentration was adjusted by controlling the secondary voltage. The generated ozone and unreacted oxygen were injected into the catalytic combustion reactor along with methane gas and nitrogen gas flows.

Figure 3 is a diagram showing the configuration of a catalytic reaction system for low-concentration methane combustion according to an embodiment of the present invention.

Referring to Figure 3, a catalyst was placed on a glass wool support layer of a 1/2 inch quartz tube to form a fixed layer. The reaction gas consisted of CH ₄ (500 ppm) + O ₃ (2,200~3,000 ppm) + O ₂ (10%) + N ₂ (Balance), and the flow rate was fixed at 53.3 ml/min and the catalyst weight was 80 mg. The w/f condition was set at 1.5 mg·min/ml. The combustion reaction was conducted in the form of an isothermal experiment by varying the catalyst fixed bed shear temperature from 75 to 225°C.

After removing unreacted ozone by connecting a hollow tube reactor heated to 225°C at the rear of the catalytic reactor, methane conversion rate and product selectivity were measured using gas chromatography (Youngin Chromatography, YL6500GC) equipped with a methanizer. Measured. Methane conversion rate and selectivity of products (CO and CO ₂ ) were calculated using the formulas below.

The separation column used in gas chromatography was Carboxen 1000 (Packed Column, 60/80 mesh, 1/8 in *15 ft, SUS tube), and the column temperature was kept constant at 150°C. At this time, 10 ml/min of N ₂ was used as the mobile phase gas, and the concentration of product and unreacted methane was quantified using a flame ionization detector (FID).

Below, the type of zeolite used in the catalyst according to this example, Cu/Al molar ratio, ozone concentration, and catalyst amount compared to the flow rate of the supplied gas will be described. Low-concentration methane combustion performance is explained in detail.

In the experiment below, low-concentration methane of 500 ppm was burned at low temperatures between 75 and 225°C at 25°C intervals using various copper ion exchange zeolite catalysts and ozone oxidizers, with the maximum combustion occurring around 150°C in most cases. Methane combustion performance was shown.

When the concentration of ozone, an oxidizing agent, was increased to 2,200-3,000 ppm for the same methane concentration (500 ppm), methane combustion performance generally tended to improve as the ozone concentration increased.

(Example 1) Comparison of low-concentration methane combustion performance according to the type of zeolite used in the catalyst

Figures 4 and 5 graphically show the low-concentration methane combustion performance of a catalyst obtained by ion-exchanging copper with a BEA-structured zeolite, and Figures 6-9 show low-concentration methane combustion performance of a catalyst obtained by ion-exchanging copper with a ZSM-5 zeolite of an MFI structure. This is a graph showing methane combustion performance.

The experimental conditions were 80 mg of catalyst and the concentration of methane supplied was set to 500 ppm. The concentration of ozone, an oxidizing agent, was adjusted to 2,500 ppm, and w/f was the same at 1.5 mg·min/ml. The horizontal axis of all drawings is the temperature value set in the isothermal reaction experiment. The vertical axes of FIGS. 4, 6, and 8 represent the conversion rate of methane, and the vertical axes of FIGS. 5, 7, and 9 represent the selectivity of the product.

Figure 4 shows the low-concentration methane combustion performance of a copper ion exchange catalyst (Cu-HBEA, molar ratio of Cu/Al 0.26) prepared using acid-type BEA zeolite with a SiO ₂ /Al ₂ O ₃ molar ratio of 25.

Referring to Figure 4, it was confirmed that the methane conversion rate improved as the temperature increased, and after 70.5% of methane was converted at 150°C, it was confirmed that the methane conversion rate decreased as the temperature increased at the temperature above.

This is because when the temperature rises above 150℃, the thermal decomposition of ozone is accelerated and the available ozone concentration decreases.

In the product selectivity shown in Figure 5, 60% of the converted methane was converted to carbon monoxide at a temperature below 100°C, but at a temperature above that, more than 70% of the converted methane was converted to carbon dioxide.

The results in Figures 4 and 5 show that when the catalyst and ozone oxidizer are applied together, very strong low-concentration methane oxidation performance can be secured at a low temperature around 150°C.

Figure 6 shows the low-concentration methane combustion performance of a copper ion exchange catalyst (Cu-HZSM-5, Cu/Al molar ratio 0.24) prepared using acid-type ZSM-5 zeolite with a SiO ₂ /Al ₂ O ₃ molar ratio of 23. .

The catalyst also shows a methane conversion rate of up to 33.1% at 175°C, and it can be seen that 50 to 100% of the converted methane was converted to carbon dioxide depending on the temperature range.

The difference in activity between the ZSM-5 catalyst and the BEA catalyst in Figure 6 appears to be due to the chemical difference in the active copper ion species developed on the catalyst.

Figures 8 and 9 show low concentration methane of a copper ion exchange catalyst (Cu-NaZSM-5, molar ratio of Cu/Al 0.24) prepared using ZSM-5 zeolite of sodium salt with a SiO ₂ /Al ₂ O ₃ molar ratio of 23. Shows combustion performance.

When comparing the catalysts in Figures 8 and 9 with the acid-type catalysts of the same structure in Figures 6 and 7, it was observed that the methane conversion rate was slightly improved at a temperature of 150°C or higher depending on the presence or absence of acid sites, but the difference was significant in terms of performance. You can't see it. In the end, it can be seen that the distribution of specific copper ion active species rather than acid points is more important in securing performance.

(Example 2) Comparison of low-concentration methane combustion performance of Cu-HBEA catalyst according to the concentration of ozone, an oxidizing agent.

Figure 10 is a graph showing low-concentration methane combustion performance as the concentration of ozone increases from 2,200 to 3,000 ppm according to 500 ppm of methane.

The catalyst used was the Cu-HBEA catalyst of Figures 4 and 5, which showed the highest methane conversion rate at 150°C, with the catalyst amount used being 80 mg and w/f set to 1.5 mg·min/ml. An experiment was performed. When comparing combustion performance according to ozone concentration, the high ozone concentration of 3,000 ppm showed the highest methane conversion rate of 49.4% at 175°C, and the methane conversion rate increased as the ozone concentration increased compared to the methane concentration. showed a trend.

The above-described embodiments of the present invention have been disclosed for illustrative purposes, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions will be possible. should be regarded as falling within the scope of the patent claims below.

Claims (7)

To burn the methane at a temperature of 125 to 175°C under conditions where the concentration ratio of methane and ozone at a low concentration of 1 volume percent or less in the atmosphere is in the range of 1:4 to 1:6, comprising SiO ₂ and Al ₂ O ₃ A zeolite catalyst in which copper is ion-exchanged to acid-type BEA zeolite, and the Cu/Al molar ratio is in the range of 0.20 to 0.30. delete delete A method for producing a zeolite catalyst for combustion of methane at a temperature of 125 to 175 ° C under conditions in which the concentration ratio of methane and ozone at a low concentration of 1 volume percent or less in the atmosphere is in the range of 1:4 to 1:6, comprising:
Converting zeolite in ammonium salt form into acid-type BEA zeolite containing SiO ₂ and Al ₂ O ₃ in which hydrogen cations are bonded to aluminum anions by heat treating them at a preset time and temperature;
Adding and stirring the acid-type zeolite to an aqueous copper nitrate solution;
separating the solid phase catalyst through a filtration device;
Washing and drying the separated solid phase catalyst; and
Comprising the step of calcining the washed and dried solid catalyst to prepare a catalyst in which copper is ion-exchanged,
A method for producing a zeolite catalyst wherein the Cu/Al molar ratio is in the range of 0.20 to 0.30. As a catalytic reaction system for low-temperature combustion of methane,
A dielectric discharge plasma (Dielectric barrier discharge, DBD) reactor that supplies ozone generated through an oxidation reaction of oxygen or air; and
An acid-type BEA zeolite containing SiO ₂ and Al ₂ O ₃ is charged with a zeolite catalyst in which copper is ion-exchanged, and methane at a low concentration of 1 volume percent or less in the atmosphere is emitted at 125 to 175° using ozone supplied from the DBD reactor. Including a catalytic combustion reactor that burns at a temperature of C,
The concentration ratio of methane and ozone is in the range of 1:4 to 1:6,
A catalytic reaction system where the Cu/Al molar ratio is in the range of 0.20 to 0.30.




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